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Lack of identification of Flaviviruses in oral and cloacal swabs from long- and short-distance migratory birds in Trentino-Alto Adige (North-eastern Italy).

Grisenti M, Arnoldi D, Rizzolli F, Giacobini M, Bertolotti L, Rizzoli A - Virol. J. (2013)

Bottom Line: All samples tested negative for Flaviviruses.The possible causes of unapparent shedding, along with ecological and epidemiological implications are discussed.The possible ecological implications are discussed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Edmund Mach Foundation, via E, Mach 1, San Michele all'Adige, Trento, Italy. michela.grisenti@fmach.it.

ABSTRACT

Background: West Nile virus (WNV) and Usutu virus (USUV), both belonging to the genus Flavivirus, are emerging in Italy as important human and animal pathogens. Migratory birds are involved in the spread of Flaviviruses over long distances, particularly from Africa to Europe. Once introduced, these viruses can be further be dispersed by short-distance migratory and resident bird species. Thus far, there is still a considerable knowledge gap on the role played by different bird species in the ecology and transmission mechanisms of these viruses. The Region of Trentino-Alto Adige (north-eastern Italy) is located on the migratory route of many of the short- and long-distance migratory birds that cross the Alps, connecting northern Europe and western Asia with southern Europe and Africa. Until now, only a silent circulation of WNV and USUV within the territory of the Province of Trento has been confirmed by serological screening, whilst no cases of infected humans or animals have so far been reported. However, continuous spillover events of both viruses have been reported in neighbouring Regions. The aim of this study was to monitor the circulation of WNV and USUV in Trentino-Alto Adige, in order to detect if active virus shedding occurs in migratory birds captured during their seasonal movements and to evaluate the role that different bird species could play in the spreading of these viruses.

Methods: We carried out a biomolecular survey on oral and cloacal swabs collected from migratory birds during seasonal migrations. Birds belonging to 18 transaharian and 21 intrapaleartic species were examined during spring (n = 176) and autumn (n = 146), and were tested using a generic nested-PCR.

Results: All samples tested negative for Flaviviruses. The possible causes of unapparent shedding, along with ecological and epidemiological implications are discussed.

Conclusions: The lack of detection of active virus shedding in these bird species does not exclude the circulation of these viruses within the Trentino-Alto Adige region, as reported in previous studies. The possible ecological implications are discussed.

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Bird sampling sites. Italian map insert: black area, sampling region of Trentino-Alto Adige; hatched area, neighbouring regions (Veneto, Lombardy, Emilia Romagna, Friuli-Venezia Giulia) with active WNV and USUV circulation.
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Figure 1: Bird sampling sites. Italian map insert: black area, sampling region of Trentino-Alto Adige; hatched area, neighbouring regions (Veneto, Lombardy, Emilia Romagna, Friuli-Venezia Giulia) with active WNV and USUV circulation.

Mentions: Taking into account the need to identify the species and the timing of WNV and USUV amplification, the absence of active shedding detected in this study may also justify the absence of clinically reportable cases of spillovers events to human and animal in Trentino-Alto Adige. Furthermore, at present, no human or animal clinical case of diseases or infections caused by Flaviviruses have been recorded in this region of Italy. Their circulation is then apparently very limited, in contrast to the high number of cases and the pathogenicity observed in animals, mosquitoes and humans in the neighbouring regions (Veneto, Lombardy, Emilia-Romagna, Friuli-Venezia Giulia: Figure 1). A possible explanation of this observed epidemiological pattern could be due to the low density of mosquitoes observed in this area as a result of a low habitat suitability for Culex spp.: a combination of low anthropization and mountainous orography of the territory, of which about 78% lies over 1,000 m above sea level, and about 55% is covered by coniferous and deciduous forests, with a temperate-oceanic climate, although a sub-Mediteranean climate can be found near Lake Garda. It is not the case that most of the detections of Flaviviruses monitored in this region were obtained in the region around Lake Garda, which provides a suitable habitat for many species of mosquitoes, including Cx. pipiens and Aedes albopictus[60,61], Rizzoli A: personal communication. This is consistent with the observation that viruses transmitted by mosquitoes are more frequently linked to mild climate, irrigated areas, wetlands and marshes with abundant mosquito and bird populations, especially migratory birds for e.g.: [16,46,47,62]. Another co-factor to be considered is the presence of a high avian biodiversity observed in the region compared to other neighbouring regions. The relationships among high host diversity and low virus spillover have been observed in several disease models, including WNV [6,63-65].


Lack of identification of Flaviviruses in oral and cloacal swabs from long- and short-distance migratory birds in Trentino-Alto Adige (North-eastern Italy).

Grisenti M, Arnoldi D, Rizzolli F, Giacobini M, Bertolotti L, Rizzoli A - Virol. J. (2013)

Bird sampling sites. Italian map insert: black area, sampling region of Trentino-Alto Adige; hatched area, neighbouring regions (Veneto, Lombardy, Emilia Romagna, Friuli-Venezia Giulia) with active WNV and USUV circulation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3852823&req=5

Figure 1: Bird sampling sites. Italian map insert: black area, sampling region of Trentino-Alto Adige; hatched area, neighbouring regions (Veneto, Lombardy, Emilia Romagna, Friuli-Venezia Giulia) with active WNV and USUV circulation.
Mentions: Taking into account the need to identify the species and the timing of WNV and USUV amplification, the absence of active shedding detected in this study may also justify the absence of clinically reportable cases of spillovers events to human and animal in Trentino-Alto Adige. Furthermore, at present, no human or animal clinical case of diseases or infections caused by Flaviviruses have been recorded in this region of Italy. Their circulation is then apparently very limited, in contrast to the high number of cases and the pathogenicity observed in animals, mosquitoes and humans in the neighbouring regions (Veneto, Lombardy, Emilia-Romagna, Friuli-Venezia Giulia: Figure 1). A possible explanation of this observed epidemiological pattern could be due to the low density of mosquitoes observed in this area as a result of a low habitat suitability for Culex spp.: a combination of low anthropization and mountainous orography of the territory, of which about 78% lies over 1,000 m above sea level, and about 55% is covered by coniferous and deciduous forests, with a temperate-oceanic climate, although a sub-Mediteranean climate can be found near Lake Garda. It is not the case that most of the detections of Flaviviruses monitored in this region were obtained in the region around Lake Garda, which provides a suitable habitat for many species of mosquitoes, including Cx. pipiens and Aedes albopictus[60,61], Rizzoli A: personal communication. This is consistent with the observation that viruses transmitted by mosquitoes are more frequently linked to mild climate, irrigated areas, wetlands and marshes with abundant mosquito and bird populations, especially migratory birds for e.g.: [16,46,47,62]. Another co-factor to be considered is the presence of a high avian biodiversity observed in the region compared to other neighbouring regions. The relationships among high host diversity and low virus spillover have been observed in several disease models, including WNV [6,63-65].

Bottom Line: All samples tested negative for Flaviviruses.The possible causes of unapparent shedding, along with ecological and epidemiological implications are discussed.The possible ecological implications are discussed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Edmund Mach Foundation, via E, Mach 1, San Michele all'Adige, Trento, Italy. michela.grisenti@fmach.it.

ABSTRACT

Background: West Nile virus (WNV) and Usutu virus (USUV), both belonging to the genus Flavivirus, are emerging in Italy as important human and animal pathogens. Migratory birds are involved in the spread of Flaviviruses over long distances, particularly from Africa to Europe. Once introduced, these viruses can be further be dispersed by short-distance migratory and resident bird species. Thus far, there is still a considerable knowledge gap on the role played by different bird species in the ecology and transmission mechanisms of these viruses. The Region of Trentino-Alto Adige (north-eastern Italy) is located on the migratory route of many of the short- and long-distance migratory birds that cross the Alps, connecting northern Europe and western Asia with southern Europe and Africa. Until now, only a silent circulation of WNV and USUV within the territory of the Province of Trento has been confirmed by serological screening, whilst no cases of infected humans or animals have so far been reported. However, continuous spillover events of both viruses have been reported in neighbouring Regions. The aim of this study was to monitor the circulation of WNV and USUV in Trentino-Alto Adige, in order to detect if active virus shedding occurs in migratory birds captured during their seasonal movements and to evaluate the role that different bird species could play in the spreading of these viruses.

Methods: We carried out a biomolecular survey on oral and cloacal swabs collected from migratory birds during seasonal migrations. Birds belonging to 18 transaharian and 21 intrapaleartic species were examined during spring (n = 176) and autumn (n = 146), and were tested using a generic nested-PCR.

Results: All samples tested negative for Flaviviruses. The possible causes of unapparent shedding, along with ecological and epidemiological implications are discussed.

Conclusions: The lack of detection of active virus shedding in these bird species does not exclude the circulation of these viruses within the Trentino-Alto Adige region, as reported in previous studies. The possible ecological implications are discussed.

Show MeSH
Related in: MedlinePlus